Dust storms seen on Mars

Before the advent of Mars-orbiting spacecraft, astronomers had a sketchy view of the Red Planet's ever-changing weather. Though Mars is one of the nearest planets to Earth, the distance between it and Earth varies greatly. The two planets circle the Sun like race cars circling a track at different speeds — and Earth "laps" Mars approximately every two years.

Martian dust storms are most likely to erupt during the Spring and early Summer in the planet's southern hemisphere — a time when Mars is closest to the Sun. Since Mars has a more elliptical orbit than Earth, its distance from the Sun varies widely. This variance causes a significant variability in the Martian climate.

Local dust storms, regional obscurations, and discrete "yellow" clouds on Mars have been reported throughout the last century; however, it is the planet-encircling dust storms that have captured our attention in the age of spacecraft exploration of Mars.

Timeline: Dust storms on Mars

1796 — Astronomer H. Flaugergues noted "yellow clouds" (now known to be clouds of dust) on Mars… as opposed to fleecy, whitish water-ice clouds.

1920 — Patchy, yellow dust clouds observed and photographed at Lowell Observatory in Arizona.

1956 — First extensive observations of a planet-encircling dust storm on Mars.

1965 — Mariner 4 conducts first fly-by of Mars; sends back dust-free photographs of a narrow swath of the planet.

1969 — Mariners 6 and 7 fly by Mars to photograph clear and cool atmospheric conditions.

1971 — The first Mars-orbiting spacecraft (Mariner 9) arrives to find the planet already shrouded in dust — the first definitive planet-wide dust storm ever seen. The dust covered everything except the poles; tall volcanic peaks poked above the dust, revealing themselves as high mountains rather than as circular basins.

1973 — Ground-based telescopes detect another planet-encircling dust storm just one Martian year after the global storm viewed by Mariner 9.

1977 — Viking spacecraft watch two planet-encircling Martian dust storms in succession from a Mars orbit and, for the first time, from the surface of Mars.

1982 — Viking Lander 1 detects what appears to be another planet-encircling dust storm just weeks before the loss of communications ends its nearly seven-year observational record on the surface of another planet.

1994 — Ground-based microwave monitoring of Mars atmospheric temperatures indicates a planet-encircling dust storm in progress, the first such planet-wide storm detected since Viking.

1997 — Mars Global Surveyor begins aerobraking at Mars and finds that planet-wide warming events can be produced by as little as a regional dust storm.

2001 — In late June the Hubble Space Telescope captures a Mars opposition photograph. (Opposition occurs when Earth lies in a straight line between the Sun and an outer planet.) The image shows seasonal dust activity in Hellas and at the North Pole. In a few weeks, these regional dust storms developed into a near-global, planet-encircling dust storm. Unprecedented details of this unusually early, blossoming storm were followed by the Mars Global Surveyor, which takes daily all-planet images and measures atmospheric temperatures.